The present invention relates to the field of network communications. In particular, the present invention relates to a system of automatic protection switching in a ring based bridged network.
The amount of data traffic being sent over metropolitan area networks (MANs) is increasing at an exponential rate. This is due in part to the increasingly ubiquitous use of the Internet by consumers and businesses, as well as the increasingly bandwidth-intensive nature of the Internet applications that are being deployed. Today""s installed MAN infrastructure is based on the Synchronous Optical NETwork (SONET), a layer-1 technology that was developed in the mid-1980s for the public telephone network and adopted by the American National Standards Institute (ANSI) as a standard for fiber optic networks. xe2x80x9cLayer-1xe2x80x9d and xe2x80x9clayer-2xe2x80x9d as used in this document refer to the OSI (Open Systems Interconnection) Reference Model. SONET has a self-healing capability in which one piece of optical fiber handles all data traffic and a second piece of optical fiber remains on standby. Should the working section fail, SONET has an automatic capability to detect the failure and transfer control to the standby section. SONET is a multiplexing technology, which means that it enforces a rigid time-division multiplexing telecom hierarchy. While this approach works well for voice traffic, it is unnecessarily expensive and inefficient for data traffic.
An alternative to using SONET as the provisioning platform for networking service is to use a bridged, layer-2 network like the Ethernet. Such networks can provide services to areas where fiber optic lines don""t extend and generally provide better data capacity at a lower cost. A problem with bus and ring networks like the Ethernet is the possibility of a single point of failure causing the system to breakdown. A common solution is to design the network with redundant segments and loops so that there is more than one route to each node in a SONET-like approach. Redundancy and loops can, however, present another problem in which a broadcast packet or an unknown unicast packet results in a broadcast storm where each node receives and rebroadcasts the packet causing potentially severe network congestion.
One way known in the industry of preventing broadcast storms and other unwanted side effects of looping is to use the Spanning Tree Protocol (STP) which has been standardized in the 802.1D specification by the Institute of Electrical and Electronic Engineers (IEEE Std. 802.1 D- 1998, IEEE Standard for Information technologyxe2x80x94Telecommunications and information exchange between systemsxe2x80x94Local and metropolitan area networksxe2x80x94Common specifications). With STP, the bridges in the network dynamically calculate an optimum subset of the topology that is loop-free and allows a path to each node. Alternate paths are blocked and unblocked as necessary to keep the routes of communication open when a fault occurs. A significant problem with STP is that when a link breaks, it may take thirty or more seconds for a path around the problem to be calculated and traffic successfully rerouted. This level of performance is too slow for use in today""s local area networks (LANs) and metropolitan area networks (MANs), for example, where the customer expects seamless connections, undetectable fault correction, and data security.
A method is provided in which an Ethernet automatic protection switching (EAPS) system prevents loops in a layer-2 network having a ring topology. The EAPS system comprises an EAPS domain having a control vlan and at least one protected data vlan. The EAPS domain is associated with a master node linked to at least one transit node in a ring network.
According to one aspect of the invention, the EAPS system operates in conjunction with the master node to detect a network failure by means of control messages sent between the nodes using the control vlan. During normal operation, the master node blocks the protected data vlan traffic from traversing its secondary port. During a network failure, the master node reroutes the protected data vlan traffic through its secondary port.
According to one aspect of the invention, when the network is restored, the EAPS system operates in conjunction with the affected transit node to prevent looping by blocking the protected data vlan traffic from traversing its restored ring port until notified by the master node that the normal operation has resumed.
According to one aspect of the invention, the master node and the transit nodes forward the EAPS control messages prior to copying them to the nodes"" CPU where among other things they are logged for use in troubleshooting.
According to one aspect of the invention, the EAPS system may be implemented on one or more network devices, such as a switch or other packet-forwarding device, a network server computer, and an end station or host computer.
In accordance with these and other aspects of the present invention, apparatus are provided for carrying out the above and other methods.